1. Technical Field
The present invention relates to a semiconductor device that is capable of transferring electric signals between two circuits to which electric signals having different potentials from each other are input.
2. Related Art
To transfer electric signals between two circuits to which electric signals having different potentials from each other are input, photo couplers are often used. Each photo coupler includes a light emitting element such as a light emitting diode and a light receiving element such as a photo transistor. The light emitting element converts an input electric signal into light, and the light receiving element returns the light to an electric signal. In this manner, photo couplers transfer electric signals.
However, it is difficult to reduce the size of each photo coupler due to the existence of the light emitting element and the light receiving element. Also, where the frequency of electric signals is high, the photo couplers cannot follow the electric signals.
Inductor elements that are formed with the use of bonding wires are disclosed in Japanese Laid-open patent publication NO. 2005-39023 and Japanese Published patent application A-H10-74625.
The present inventors have recognized as follows. To transfer electric signals between two circuits to which electric signals having different potentials from each other are input, electric signals are transferred by inductively coupling the two inductors to each other. In this case, to reduce transmission errors, the coefficient of coupling between the inductors needs to be made larger. To form the two inductors that are inductively coupled to each other, spiral inductors may be stacked on each other. However, spiral inductors are often formed with interconnect layers of a semiconductor device. Therefore, it is difficult to increase the diameter of each inductor. As a result, the coefficient of coupling between two inductors cannot be made larger.